Enteric bacteria such as Escherichia coli and Salmonella species are principal causative agents of diarrhea, dysentery, urinary tract infections, meningitis in children, septicemia, enteric fevers, an pneumonia. They are primary causes of infant mortality, malnutrition and retarded mental and physical development worldwide. They ar primary causes of infant mortality, malnutrition and retarded mental and physical development worldwide. They are also the organisms that have been most extensively studied, ar the best understood at the molecular level, and are most amenable to physiological, genetic, and biochemical manipulation. They serve as prototypes for the establishment of basic biological principles and the study of universal biological functions. In spite of these facts, major gaps exist in our understanding of their metabolic and genetic regulatory mechanisms. The phosphoenolpyruvate:sugar phosphotransferase system (PTS) is a complex transport, kinase and regulatory system which in E. coli controls the utilization of numerous carbon and nitrogen sources not taken up via the PTS-catalyzed group translocation mechanism. About 1% of all E. coli genes encode PTS proteins, emphasizing the importance of th PTS to the organism. Studies in our laboratory have allowed us to: (1) define the allosteric mechanism by which PTS-mediated protein phosphorylation regulates the activities of non-PTS carbohydrate permeases and catabolic enzymes; (2) propose an allosteric mechanism by which adenylate cyclase is regulated by the PTS; (3) demonstrate that the fructose repressor (FruR) mediates cAMP- independent catabolite activation/repression, regulating transcription of numerous genes encoding proteins involved in pathogenesis ad central pathways of carbon metabolism; (4) identify PTS protein homologues (ILA Ntr and NPr) encoded within the rpoN operon of E. coli that appear to coordinate nitrogen utilization with carbon availability by influencing sigma54-dependent transcription, and (5) provide evidence that several global regulatory systems interact to form a regulatory network. Our long-range goals are to understand the involvement of the PTS and PTS auxillary proteins in the regulation of carbon and nitrogen metabolism, and to define the mechanisms by which global regulatory proteins (e.g., PTS proteins, FruR, adenylate cyclase, ILANu, CRP, Fnr) interact to form complex regulatory network. Our specific goals are to: (1) utilize biochemical techniques recently developed in our laboratory to establish the mechanism of PTS-mediated adenylate cyclase regulation; (2) use molecular genetic techniques to establish the mechanisms of FruR-mediated transcriptional regulation; and (3) characterize the mechanisms by which the PTS, ILANu and other rpoN operon-encoded proteins influence the transcription of sigma54-dependent genes. The proposed studies are expected to provide basic information regarding complex regulatory mechanisms in E. coli and other enteric bacteria that will be of use in the control of these pathogens and will be universally applicable to an understanding of regulatory phenomena in all living cells.